1. Field of the Disclosure
This disclosure is related to a backlight unit, and particularly to a light driver capable of preventing a current deviation between a plurality of lamps which are connected to one another in the backlight unit.
2. Description of the Related Art
A cathode ray tube (CRT) is one among a wide number of display devices and is mainly employed in the monitors of television receivers, measuring instruments, and information terminals. (I don't understand what you mean by ‘information terminals’) It is difficult to apply the CRT to small and light electronic products, because of its weight and size. In other words, the CRT has a limit due to its weight and size while the trend for electronic products is to be light-weight and small in size.
To address this matter, a liquid crystal display (LCD) device using an electro-optical effect, a plasma display panel (PDP) using a gas discharge, and an electro-luminescent display (ELD) device using an electro-luminescent effect are expected to substitute for the CRT. Among these devices, the LCD device has actively been developed.
The LCD device controls an amount of incident light from the exterior in order to display a picture. The LCD device necessarily requires a separate light source, such as a backlight unit, irradiating on the LCD panel because it is a light receiving device. The backlight unit employed in the LCD device as the light source can be classified as either an edge type or a direct type in accordance with the disposition of a cylindrical emission lamp.
The edge type backlight unit includes a lamp unit on the side surface of a light guide panel guiding light. The lamp unit includes a light emitting lamp, lamp holders receiving both ends of the lamp in order to protect the lamp, and a lamp reflection plate reflecting light emitted from the lamp toward the light guide panel. The lamp reflection plate surrounds the outer circumferential surface of the lamp and has an edge portion which is inserted in the side surface of the light guide panel.
Such an edge type backlight unit with the lamp unit installed on the side surface of the light guide panel is mainly applied to comparatively small-sized LCD devices such as the monitors of laptops and desk-top computers. The edge type backlight unit has good light uniformity, a lengthened lifespan, and the advantage of thinning the LCD device.
The direct type backlight unit has begun to be concentrically developed as the LCD device is enlarged to a size above 20 inches. The direct type backlight unit forces light to be irradiated onto the entire surface of the LCD panel. To this end, the direct type backlight unit includes a plurality of lamps arranged in a row (or side by side) on the inner surface of a bottom cover.
Since the direct type backlight unit has a higher light efficiency than the edge type backlight unit, it is mainly used for LCD devices of a large size which require a high brightness.
In such a direct type backlight unit, the plural lamps arranged at a constant distance are electrically connected to an external inverter, which is installed on the outside of the backlight unit, via a common electrode. In other words, the plural lamps are connected parallel to one another.
The inverter includes a transformer applying an electric power of alternating current to an output terminal and a balance capacitor disposed between the secondary terminal of the transformer and the end terminals of the lamps. The balance capacitor controls an electric current to be applied to each lamp and uniformly balances the electric current. Also, the balance capacitor matches the lamps and the output side of the inverter in impedance.
However, the electric current applied to each of the lamps is not uniform when the related art backlight unit is driven by the inverter. This results from an unbalance between the impedance components of the balance capacitor and an equivalent capacitor of the lamp. In other words, although the related art backlight unit includes the balance capacitor, it does not maintain a uniform brightness in each region.